1. Field of the Invention
The invention relates in general to a method of adjusting gain balance of an optical transducer, and more particularly to an adjusting method of balancing the gain in an optical transducer for receiving reflected light in an optical drive.
2. Description of the Related Art
In an optical drive, a micro light spot with the diameter ranging from about 0.85 to 2.11 microns is projected onto an optical disk, and the reflected light being reflected from the optical disk is received. By making use of an electric signal which is generated according to different light amount of the reflected light, the optical drive which is servo-controlled is able to read the data on the optical disk. Because the reflection spot of the reflected light is very small, the converted electric signal is relatively weak. Therefore, the signal is needed to be amplified with a gain, and the reflection spot is needed to be projected on the receiving position in a balanced manner, so as to enhance the signal quality and reliability.
FIG. 1 (Prior Art) is a schematic illustration showing that the gain balance of the optical transducer is adjusted in a conventional optical drive 10. The conventional optical drive 10 utilizes an optical system having an optical pick-up head 11 to focus a light beam emitted from a laser photodiode 12 into the micro light spot, and to project the light beam on a rotating optical disk 13. The optical disk 13 reflects the light beam back to the optical pick-up head 11, and projects it on an optical transducer 14 to form a reflection spot 15. The optical transducer 14 is divided into a left half portion and a right half portion, which have the same size and respectively have gains G1 and G2. The left half portion and the right half portion of the optical transducer 14 each receives a portion of the reflection spot 15, and converts the corresponding luminous flux, which is induced from the reflection spot 15 being received thereon, into the current signal with corresponding level. Then, the converted weak currents are properly amplified by the gains G1 and G2, respectively, so as to facilitate the subsequent signal processing.
The optical drive 10 adjusts the gain balance of the optical transducer before the operation of tracking servo. The optical drive 10 utilizes an actuator 16 to move a set of objective lens 17, so as to adjust the position where the reflection spot 15 is projected on the optical transducer 14. When the reflection spot 15 is equally projected on the left and right half portions of the optical transducer 14, which means that the light receiving areas of the left and right half portions are the same, the difference between the received amounts of the reflected light can be thus eliminated. In this regard if we let the left and right half portions of the optical transducer 14 only have different gains on the circuit, we may also need to provide an external gain modulation device 18 with a corresponding external gain Kb. If the value of the external gain Kb can be properly used, the current signals, outputted from the left and right half portions of the optical transducer 14 after being amplified by their respective gains, can be gain-balanced. As a result, the output value, which is obtained by subtracting the current signals being gain-balanced from each other, will be equal to 0, and the optical signals of the left and right half portions will be balanced. Thereafter, when the optical disk is read/written in a tracking manner, the optical drive is servo-controlled to read the data on the optical disk according to variations of the differences between the optical signals, which are detected by the left and right half portions of the optical transducer 14.
However, the projection position of the micro reflection spot 15 being projected on the optical transducer 14 is inside the optical drive 10, so that the projection position cannot be adjusted with human eyes, and only can be judged according to the output signal. Because the different signal circuits have differences gains, the reflection spot 15 may be not projected on the middle of the optical transducer 14 after adjusting. Thus, the light receiving areas of the left and right half portions of the optical transducer 14 are not the same, and the difference of the received reflected light cannot be eliminated. Moreover, the signal levels outputted from the left and right half portions of the optical transducer 14 are relative to the difference between the light receiving areas thereof. So, in the conventional method of adjusting the gain balance of the optical transducer in the optical drive, the balance value cannot be obtained by simply calculating the external gain Kb with respect to the equation G1*Kb=G2 according to the gains' difference, but needs to be obtained by repeatedly adjusting and testing. In addition, due to the different light receiving areas, the obtained external gain Kb may fail in ensuring that the reflection spot 15 can be projected on the middle of the optical transducer 14. Thus, it may be not possible to correctly present the variation of the difference between the light signals detected by the two half portions of the optical transducer 14, thereby reducing the signal quality and reliability. Therefore, the conventional optical transducer still has problems to be solved in the aspect of gain balance adjustment.